Power train control system

ABSTRACT

A power train control ( 1 ) for a vehicle ( 8 ) or an automotive machine with a prime mover ( 5 ) with a governor ( 2 ) and a continuously variable transmission ( 7 ) with a ratio control ( 3 ). The power train control ( 1 ) coordinates the ratio control and the governor issuing a theoretical speed n_mot_nom to the governor ( 2 ) for the prime mover ( 5 ) and a nominal transmission ratio i_nom to the ratio control ( 3 ). The power train control ( 1 ) is designed as a combination of two governors, the transmission output speed governor ( 9 ) and the governor ( 10 ) for relief of the prime mover ( 5 ). The transmission output speed governor ( 9 ) receives the transmission output speed n_out as a control variable and generates the nominal speed n_mot_nom for the prime mover ( 5 ) as a manipulated value, and the governor ( 10 ) for relief of the prime mover ( 5 ) by the speed n_mot of the prime mover ( 5 ) as a control value and a transmission ratio correction value Δi as a manipulated value. The nominal transmission ratio i_nom is specified by addition of this correction value Δi to a coarse transmission nominal ratio i_0_nom, with the latter being specified as function of the nominal speed n_mot_nom of the prime mover ( 5 ) and the nominal transmission output speed n_out_nom set by the driver ( 4 ).

BACKGROUND OF THE INVENTION

The invention refers to a power train control for overall control of aprime mover and a transmission for a vehicle or an automotive machinewith a prime mover with speed control and a continuously variabletransmission with ratio control.

SUMMARY OF THE INVENTION

A power train control for a tractor management system is outlined in anarticle by A. Jaufmann, O+P Ölhydraulik und Pneumatik41 (1997) Nr. 4,234-241. Details regarding control and regulation strategies oralgorithms for the management of the complete system made up of primemover and transmission, however, are not dealt with.

The objective of the invention is to come up with a power train controlwhich controls a power train including the components prime mover withspeed governor and CVT with ratio control in such a way that minimumenergy is consumed, but the performance/traction required is availablewhen needed. The transitions between the set combinations of speed ofprime mover and gear ratio are to be effected promptly and in a stablemanner.

This task is solved by means of a generic power train control which isalso provided with the characteristic features of the main claim.

Specific versions of the invention are detailed in the sub-claims.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of a version of the invention is detailed in the followingwith the aid of schematics and functional diagrams.

FIG. 1 Block diagram showing the integration of the power train controlsystem into the overall vehicle system.

FIG. 2 Schematic of the power train control system with transmissionoutput speed governor and the governor for prime mover relief.

FIG. 3 Schematic of the transmission output speed governor.

FIG. 4 Characteristics of operands of the transmission output speedgovernor for determination of its manipulated variable, the nominalspeed n_mot_nom of the prime mover.

FIG. 5 Schematic of the governor for prime mover relief.

FIG. 6 Characteristics of operands of the governor for prime moverrelief for determination of its manipulated variable, the nominaltransmission ratio i_nom.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The power train control system 1 is a higher-order software unitsupplying nominal values to the lower-order control loops governor 2 ofthe prime mover 5 and ratio control 3 of the continuously variabletransmission 7 (FIG. 1). It supplies a nominal speed n_mot_nom to thegovernor 2 of the prime mover 5 and a nominal transmission ratio i_nomto the ratio control 3. To avoid division by zero, a nominal value forreciprocal transmission may be used instead of the transmission rationominal value i_nom. All following calculations are performed as analogcomputations with the reciprocal transmission ratio i_rec and itsderived analog operands instead of with the transmission ratio i and allits derived operands. The reciprocal transmission ratioi_rec=n_output/n_input is preferred especially for continuously variablepower-splitting transmissions, since with this type of transmission theoutput speed zero may be set for certain transmission settings and afinite input speed, as a result of the two power-split ranges beingsummarized in a summarizing transmission. This zero setting (zerodivision), i. e. an infinite transmission ratio, is avoided with the useof the reciprocal transmission ratio.

To compute these nominal values, the power train control system 1processes at least the following input parameters:

The nominal transmission output speed n_outnom, which is proportional tothe nominal road speed set by the driver 4. The (actual)transmissionoutput speed n_out. The (actual)speed n_mot of the prime mover 5. Theload signal p_vol of the governor 2 of the prime mover 5 .

The governor 2 of the prime mover 5 supplies the latter with the signalfor the injection volume or load p_vol, for the desired speed of theprime mover 5 to be maintained as far as possible. The ratio control 3supplies the transmission 7 with various transmission-specific controlsignals 6, for the desired transmission connection to be establishedbetween prime mover 5 and vehicle 8.

The power train control system 1 (FIG. 2) is designed to supply theprime mover 5 with the performance required for the nominal drive speedat minimum engine speed. With regard to efficiency, this is veryfavorable, because in this manner the power train is operated at anear-optimum degree of efficiency. The power train control system 1 isrealized as a combination of two governors, the transmission outputspeed governor 9 and the governor 10 for the relief of the prime mover5. The regulating mechanisms of the two governors operate simultaneouslyand supplement each other. The transmission output speed governor 9 ischaracterized by the transmission output speed n_out as a controlledvariable and by the nominal speed n_mot_nom of the prime mover 5 as amanipulated variable. The controlled variable of the governor 10 for therelief of the prime mover 5 is the speed n_mot of the prime mover 5. Itsmanipulated variable is an offset value Δi for the coarse transmissionnominal ratio i_(—) 0_nom, which is preset in a processing unit 11 onthe basis of nominal drive speed and nominal speed n_mot_nom of theprime mover 5.

The performance requested is determined by the transmission output speedgovernor 9 by comparing nominal and actual output speeds (FIG. 2).Additional correction of the manipulated value n_mot_nom is provided bythe influence of the load signal p_vol of the governor 2 of the primemover 5. Initially, the transmission output speed governor 9 provides alow nominal speed n_mot_nom for the prime mover 5. For low performancerequirements, the specified nominal transmission output speed n_out_nomcan be maintained.

Transmission output speed n_out will decrease with increasingperformance requirements. The transmission output speed governor 9 willthen increase the nominal speed n_mot_nom of the prime mover 5 until,due to the raised input performance, the transmission output speed n_outhas returned to its nominal value nout_nom.

In the processing unit 11, the provisional coarse transmission nominalratio i_(—) 0_nom is computed from the nominal speed n_mot_nom of theprime mover 5 on the basis of the equation i _(—)0_nom=n_mot_nom/n_out_nom. This provisional value i _(—) 0_nom is inputvalue for the governor 10 for relief of the prime mover 5, where it iscorrected and becomes the final nominal transmission ratio i_nom.Correction is determined by the deviation of the actual speed of theprime mover 5 from its nominal speed (n_mot_nom−n_mot), the so-calledprime mover 5 depression. With prime mover 5depression(n_mot<n_mot_nom), the ratio is corrected to a lower ratio, i.e. to higher nominal ratio figures i_nom. When the prime mover 5 israced (n_mot>n_mot_nom), the ratio is corrected to a higher ratio, i. e.to lower nominal ratio figures i_nom. This correction is necessarybecause of the highly dynamic coarse transmission nominal ratio i _(—)0_nom. For this nominal value is computed on the basis of the nominaltransmission output speed n_out_nom, which is directly specified by thespeed set by the driver 4. The driver 4, however, can instantaneouslychange his specified speed, which will immediately change the nominalratio. Rapid changes toward high ratios will result in the transmission7 bringing high drag forces to bear on the prime mover 5. Due toinertia, the vehicle 8 will more or less maintain its speed, while theratio change will almost exclusively find its expression in a depressionof the speed of the prime mover 5. The governor 2 of the prime mover 5is not capable of maintaining the speed n_mot_nom at the prime mover 5as specified by the power train control system 1. Depending on the speedload, the prime mover 5 might even be stalled. By analogy, a rapidchange (re-setting) to low ratios may have a strong propelling effect onthe prime mover 5. The governor 10 for the relief of the prime mover 5uses the course transmission nominal ratio i _(—) 0_nom to calculate thecorrected value i_nom, which is passed on to the ratio control 3 of thetransmission 7. On the basis of the corrected ratio, the governor 2 ofthe prime mover 5 is in a position to more or less maintain the nominalspeed n_mot_nom on the prime mover 5 as specified by the power traincontrol system 1. Correction of i _(—) 0_nom consequently relieves theprime mover 5. Therefore, this governor 10 has been termed “governor forthe relief of the prime mover”.

A detailed description of the transmission output speed governor 9follows:

The transmission output speed governor 9 is essentially aproportional/integral governor 12 (FIG. 3). Proportional and integralshares of the manipulated value n_mot_nom each possess a non-lineardependence on the system deviation n_out_nom−n_out. Moreover, both theintegral share and the overall manipulated value possess arate-of-change limiter (hill-climbing controller) and an absolute-valuelimiter. The proportional share n_mot_nomprop of the manipulated valuen_mot_nom as well as the temporal derivative of its integral sharen_mot_nomip are each determined by means of characteristics depending onthe system deviation n_out_nom−n_out (FIG. 4). In an integrator 13, thetemporal derivative n_mot_nom_ip of the integral share n_mot_nom_i ofthe manipulated value n_mot_nom is integrated into an absolute integralshare n_mot_nom_i, with the following limiters being operative:Integration is discontinued when the integral share n_mot_nom_i hasreached a value of n_mot_nom_i_b1 for a bottom limit or a valuen_mot_nom_i_u1 for an upper limit. This means,n_mot_nom_i_b1≦n_mot_nom_i≦n_mot_nom_i_u1 always applies.

Moreover, the temporal derivative n_mot_nom_ip of the integral sharen_mot_nom_i of the manipulated value n_mot_nom is limited by a minimumvalue n_mot_nom_ip_b1. The minimum value n_mot_nom_ip_b1 is specifiedfor the prime mover 5 as characteristics depending on the relative loadp_vol_rel (FIG. 4). The relative load p_vol_rel is the quotientresulting from the division of the load signal pvol by thespeed-dependent full load p_vol_max of the prime mover 5:p_vol_rel=p_vol/p_vol_max.

The values of p_vol_max as functions of the engine speed n_mot aretuning parameters in relation to the prime mover 5.

As a result of rate-of-change limitation, n_mot_nom_ip_b1 ≦n_mot_nom_ipis always maintained.

The two governor shares n_mot_nom_i and n_mot_nom_prop are added upresulting in a specification value n_mot_nom_(—)0 for the speedn_mot_nom of the prime mover 5. This summarized value n_mot_nom_(—)0 isfiltered by a time-delay element 14 (PT1-element) with rate-of-changeand absolute-value limiters. The limiters ensure that the followingconditions are always maintained for the final manipulated valuen_mot_nom of the transmission output speed governor 9 as well as fortheir temporal derivatives:

n_mot_min≦n_mot_nom≦n_mot_max and

n_mot_nom_p_min≦n_mot_nom_p <n_mot_nom_p_max

with

n_mot_min being a specified min. value of the nom. speed n_mot_nom ofthe prime mover 5 and

n_mot_max being a specified max. value of the nom. speed n_mot_nom ofthe prime mover 5

and with

n_mot_nom_p_min being a specified min. value of the temporal derivativen_mot_nom_p of the nominal speed n_mot_nom of the prime mover 5 and

n_mot_nom_p_max being a specified max. value of the temporal derivativen_mot_nom_p of the nominal speed of the prime mover 5.

As a rule, the specified min. value n_mot nom_p_min of the temporalderivative n_mot_nom_p of the nominal speed of the prime mover 5 isalready specified by the limit value n_mot_nom_ip_b1 used above forn_mot_nom_ip. As a rule, n_mot_nom _p_max is a fixed limit specified astuning parameter.

A detailed description of the governor 10 for the relief of the primemover 5 follows:

As mentioned above, correction of the coarse transmission nominal ratioi_(—) 0_nom by the governor 10 for the relief of the prime mover 5 tothe output value i_nom for the ratio control 3 of the transmission 7 iseffected mainly for dynamical reasons. The most important task of thegovernor 10 for the relief of the prime mover 5 is correction of there-setting speed d/dt(i _(—) 0_nom) of the coarse transmission nominalratio i _(—) 0_nom. Therefore, correction of the coarse transmissionnominal ratio i _(—) 0_nom is carried out only on gradients (FIG. 5).Gradient calculation by a PT1-element 15 determines a non-correctedsetting speed i_nom_point_desire:

i_nom_point_desire=(1/τ_i_nom_desire)*(i_(—) 0_nom−i_nom), with the timeconstant τ_i_nom_desire being a tuning parameter. This means,i_nom_point_desire follows, smoothened by the PT-1 filter, the dynamicswith which the transmission output speed governor 9 specifies thenominal speed n_mot_nom for the prime mover 5. i_nom_point_desire islimited by the tuning parameters i_nom_point_desire_min andi_nom_point_desire_max:

i_nom_point_desire_min≦i_nom_point_desire≦i_nom_point_desire_max.

The actually effective setting speed i_nom_point results in a correctionelement 16 from the summing-up of i_nom_point_desire with the twocorrection terms i_nom_point_prop and i_nom_point_diff:

i_nom_point=i_nom_point_desire+i_nom_point_prop+i_nom_point_diff.

i_nom_point_prop and i_nom_point_diff represent the proportional anddifferential shares of the governor 10 for the relief of the prime mover5 and are specified by characteristics (FIG. 6) depending on the systemdeviation diff_n_mot=n_mot_nom−n_mot and/or their filtered temporalderivative diff_n_mot_point_filt=filter function (d/dt(n_mot_nom−n_mot).

Integration of the summarized value i_nom_point in an integrator 17finally results in the final nominal value i_nom, supplied by the powertrain control system 1 to the ratio control 3 of the continuouslyvariable transmission.

As a rule, the correction term does not alter the setting direction ofthe transmission ratio. Only the setting speed is reduced, i. e. i_nomapproaches i_(—) 0_nom at a slower rate when the prime mover 5 isdepressed or raced. In an extreme situation, however, such as a suddenchange to a very high drive drag, the correction term may overcompensatethe non-corrected setting speed i_nom_point_desire. This means thatsetting is effected not only at a slower rate to low ratios i, butexplicitly to high ratios i.

As mentioned above, all calculations can be analog computations with thereciprocal transmission ratio i_rec and its analog derivatives insteadof with the transmission ratio i and all its derivatives. Of coarse, thederived parameters are to be newly determined and mathematicallycorrect.

References

1 power train control

2 governor (of the prime mover)

3 ratio control

4 driver

5 prime mover

6 control signals

7 transmission

8 vehicle

9 transmission output speed governor

10 governor (for relief of the prime mover)

11 processing unit

12 proportional/integral governor

13 integrator

14 time-delay element

15 pt1-element

16 correction element

17 integrator

What is claimed is:
 1. A power train control system connected to a primemover (5), controlled by a prime mover governor (2), with the primemover being connected to a continuously variable transmission (7) whichis controlled by a ratio control (3), the power train control systemcomprising: a combination of a transmission output speed governor (9)and a governor (10) for relief of the prime mover, and the power traincontrol system (1) comprising means for issuing a theoretical primemover speed n_mot_nom to the prime mover governor (2) and for issuing atheoretical transmission ratio i_nom to the ratio control (3); thetransmission output speed governor (9) receiving, as a control variableinput, the transmission output speed n_out, and outputting, as amanipulated variable of the transmission output speed governor (9), thetheoretical prime mover speed n_mot_nom; the governor (10) for relief ofthe prime mover receiving, as a control variable input, the speed n_motof the prime mover (5), and outputting, as a manipulated variable of thegovernor (10) for relief of the prime mover, a transmission ratiocorrection value Δi, with the theoretical transmission ratio i_nom beingcalculated by adding the correction value Δi to the initial transmissiontheoretical value i_(—) 0_nom; and the initial transmission theoreticalvalue i_(—) 0_nom is determined as a function of the theoretical primemover speed n_mot_nom of the prime mover (5) and the theoreticaltransmission output speed n_out_nom.
 2. The power train control (1)according to claim 1, wherein the transmission ratio theoretical valuei_(—) 0_nom is specified by the equation: i _(—)0_nom=n_mot_nom/n_out_nom.
 3. The power train control (1) according toclaim 1, wherein both the transmission output speed governor (9) and thegovernor (10) for relief of the prime mover are digital ProportionalIntegral Derivative (PID) governors.
 4. The power train control (1)according to claim 1, wherein the transmission output speed governor (9)is a Proportional Integral (PI) governor and a proportional valuen_mot_nom_prop and an integral value n_mot_nom_i of the manipulatedvariable n_mot_nom each have a non-linear dependence on a systemdeviation n_out_nom.
 5. The power train control (1) according to claim4, wherein the proportional value n_mot_nom_prop of the manipulatedvalue n_mot_nom as well as a temporal derivative n_mot_nom_ip of theintegral value n_mot_nom_i are each determined by means of thecharacteristics depending on the system deviation n_out_nom−n_out. 6.The power train control (1) according to claim 5, wherein the integralvalue n_mot_nom_i of the manipulated value n_mot_nom is limited so thatthe following relationship always applies:n_mot_nom_i_b1≦n_mot_nom_i≦n_mot_nom_i_u1, where n_mot_nom_i_b1 is abottom limit for the value n_mot_nom_i and n_mot_nom_i_u1 is an upperlimit for the value n_mot_nom_i.
 7. The power train control (1)according to claim 5, wherein the temporal derivative n_mot_nom_ip ofthe integral value n_mot_nom_i of the manipulated value n_mot_nom islimited by a minimum value n_mot_nom_ip_b1.
 8. The power train control(1) according to claim 7, wherein the minimum value n_mot_nom_ip_b1 isspecified by a characteristic curve depending on a relative loadp_vol_re1 of the prime mover (5), and the relative load p_vol_re1 is aquotient determined from a load signal p_vol and a speed-dependent fullload p_vol_max of the prime mover (5) and the speed-dependent full loadp_vol_max is a tuning parameter of the prime mover (5).
 9. The powertrain control (1) according to claim 1, wherein the manipulated value ofthe transmission output speed governor (9) n_mot_nom is filtered by atime-delay element (14).
 10. The power train control (1) according toclaim 9, wherein the time-delay element (14) is a PT1-element withrate-of-change and absolute value limiters.
 11. The power train control(1) according to claim 1, wherein the manipulated value of thetransmission output speed governor (9) n_mot_nom fulfills a relation of:n_mot_min≦n_mot_nom≦n_mot_max, where n_mot_min is a specified minimumvalue of the nominal speed n_mot_nom of the prime mover (5) andn_mot_max is a specified maximum value of the nominal speed n_mot_nom ofthe prime mover (5).
 12. The power train control (1) according to claim1, wherein a temporal derivative of the manipulated value n_mot_nom_pfulfills a relation of: n_mot_nom_p_min≦n_mot_nom_p≦n_mot_nom_p_max,where n_mot_nom_p_min is a specified minimum value of the temporalderivative n_mot_nom_p of the nominal speed n_mot_nom of the prime mover(5) and n_mot_nom_p_max is a specified maximum value of the temporalderivative n_mot_nom_p of the nominal speed of the prime mover (5). 13.The power train control (1) according to claim 12, wherein the specifiedminimum value n_mot_nom_p_min of the temporal derivative n_mot_nom_p ofthe nominal speed of the prime mover (5) is set by the valuen_mot_nom_ip_bl.
 14. The power train control (1) according to claim 1,wherein the governor (10) for relief of the prime mover uses a coarseresetting speed d/dt (i_(—) 0_nom) to calculate a corrected resettingspeed i_nom_point, and the coarse resetting speed d/dt (i _(—) 0_nom) isdetermined by a temporal derivative of the initial transmission rationtheoretical value i _(—) 0_nom computed in the processing unit (11) on abasis of the theoretical prime mover speed n_mot_nom from thetransmission output speed governor (9) and a theoretical transmissionoutput speed n_out_nom from a driver (4), and integration of thecorrected resetting speed in the governor (10) for relief of the primemover results in the theoretical transmission ratio i_nom.
 15. The powertrain control (1) according to claim 14, wherein the governor (10) forrelief of the prime mover contains a proportional/differential governorwhich sets the corrected resetting speed i_nom_point.
 16. The powertrain control (1) according to claim 15, wherein the resetting speedi_nom_point is specified by the relation of:i_nom_point=i_nom_point_desire+i_nom_point_prop+i_nom_point_diff, wherei_nom_point_desire is a function of i_(—) 0_nom and i_nom, andi_nom_point_prop represents a proportional share of the governor (10)for relief of the prime mover and is specified by a characteristic curvedepending on the system deviation diff_n_mot=n_mot_nom−n_mot, andi_nom_point_diff represents a differential share of the governor (10)for relief of the prime mover and is specified by a characteristic curvedepending on the filtered temporal derivative of the system deviationdiff_n_mot_point_filt=filter function (d/dt (n_mot_nom−n_mot).
 17. Thepower train control (1) according to claim 16, whereini_nom_point_desire is specified by the relation of:i_nom_point_desire=(1/τ_i_nom_desire)*(i_(—) 0_nom−i_nom), where thetime constant τ_i_nom_desire is a tuning parameter.
 18. The power traincontrol (1) according to claim 16, wherein i_nom_point_desire is limitedby the relation of:i_nom_point_desire_min≦i_nom_point_desire≦i_nom_point_desire_max, wherei_nom_point_desire_min and i_nom_point_desire_max are tuning parameters.19. A power train control system connected to a prime mover (5),controlled by a prime mover governor (2), with the prime mover beingconnected to a continuously variable transmission (7) which iscontrolled by a ratio control (3), the power train control systemcomprising: a combination of a transmission output speed governor (9)and a governor (10) for relief of the prime mover, and the power traincontrol system (1) comprising means for issuing a theoretical primemover speed n_mot_nom to the prime mover governor (2) and for issuing atheoretical transmission ratio i_nom to the ratio control (3); thetransmission output speed governor (9) receiving, as a control variableinputs, the transmission output speed n_out, a load signal p_vol and atheoretical transmission output speed n_out_nom and outputting, as amanipulated variable of the transmission output speed governor (9), thetheoretical prime mover speed n_mot_nom; the governor (10) for relief ofthe prime mover receiving, as a control variable inputs, the speed n_motof the prime mover (5), an initial transmission theoretical value i_(—)0_nom, and the theoretical prime mover speed n_mot_nom of the primemover (5), and outputting, as a manipulated variable of the governor(10) for relief of the prime mover, a theoretical transmission ratioi_nom and determining a transmission ratio correction value Δi, with thetheoretical transmission ratio i_nom being calculated by adding thecorrection value Δi to the initial transmission theoretical value i _(—)0_nom; and the initial transmission theoretical value i_(—) 0_nom isdetermined as a function of the theoretical prime mover speed n_mot_nomof the prime mover (5) and the theoretical transmission output speedn_out_nom.